I agree, there are a lot of people that can both very well and to be honest most contractors have to be able to if they want to get work.

I don't think that the skill set required is actually that different, but your right in saying discipline is required in order to excel in both.

Then I think the key point is those that do possess both skills and the discipline/drive to excel at both are usually either doing very well doing their own thing and aren't looking for work.